Semiconductor device having a fin structure and a manufacturing method thereof

ABSTRACT

Provided is a semiconductor device including: a fin structure on a substrate including a negative channel field-effect transistor (nFET) region and a positive channel field-effect transistor (pFET) region; a gate structure on the fin structure; and a source/drain structure adjacent to the gate structure, wherein the source/drain structure formed in the nFET region is an epitaxial layer including an n-type impurity at a concentration of about 1.8×1021/cm3 or more, includes silicon (Si) and germanium (Ge) on an outer portion of the source/drain structure, and includes Si but not Ge in an inner portion of the source/drain structure, wherein an inclined surface contacting an uppermost surface of the source/drain structure forms an angle of less than about 54.7° with a top surface of the fin structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C § 119 toKorean Patent Application No. 10-2017-0082910, filed on Jun. 29, 2017,in the Korean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a semiconductor device, and moreparticularly, to a semiconductor device including a fin field effecttransistor (FinFET).

In order to realize high-capacity and highly integrated devices,semiconductor devices have been continuously scaled down. Criticaldimensions including minimum features sizes of semiconductor deviceshave been reduced for increasing a density of the semiconductor devices.However, in a semiconductor device having a two-dimensional (2D) planarstructure, a short channel effect may limit scaling down of thesemiconductor devices because a length of a horizontal channel may beshortened as the size of the semiconductor device is reduced. To addressthis short channel effect, a fin field-effect transistor (FinFET) havinga fin structure has been introduced. The structural characteristics ofthe FinFET may prevent the short channel effect by securing an effectivechannel length and increase an operating current magnitude by increasinga channel width.

SUMMARY

An aspect of the inventive concept according to exemplary embodimentsprovides a realization of a semiconductor device having excellentelectrical characteristics and manufacturing efficiency.

Aspects of the inventive concept should not be limited by the abovedescription, and other unmentioned aspects will be clearly understood byone of ordinary skill in the art from example embodiments describedherein.

According to an aspect of the inventive concept, there is provided asemiconductor device including: a fin structure on a substrate includinga negative channel field-effect transistor (nFET) region; a gatestructure formed on the fin structure; and a source/drain structureformed adjacent to the gate structure, the source/drain structure beingformed with an epitaxial layer n-type impurity, the concentration of then-type impurity is about 1.8×10²¹/cm³ or more, and the outer portion ofthe source/drain structure including silicon (Si) and germanium (Ge),and the inner portion of the source/drain structure including Si but notGe, and wherein an inclined surface portion of an uppermost surface ofthe source/drain structure forms an angle of less than about 54.7° witha top surface of the fin structure.

According to another aspect of the inventive concept, there is provideda semiconductor device including: a fin structure disposed on asubstrate; a gate structure on the fin structure; and a source/drainstructure adjacent to the gate structure, wherein the source/drainstructure forms a source/drain assembly in which adjacent source/drainstructures are merged with each other via a (110) crystal surface andthe source/drain assembly includes a different material on an outerportion of the source/drain assembly which is not included in an innerportion of the source/drain assembly.

According to another aspect of the inventive concept, there is provideda semiconductor device including a fin structure on a substrateincluding the nFET region and the pFET region; an element isolatinglayer between the fin structures; a gate structure on the fin structure;and a source/drain structure adjacent to the gate structure, wherein thesource/drain structure formed in the nFET region includes: a top patternof the fin structure which is a portion of the fin structure protrudingover the element isolating layer; and a selective epitaxial growth (SEG)portion formed on a top surface and side surfaces of the top pattern ofthe fin structure, wherein an angle between an inclined surface portionof an uppermost surface of the SEG portion and the top surface of thetop pattern of the fin structure is less than about 54.7°, and the SEGportion includes Si and Ge on an outer portion of the SEG portion andincludes Si but not Ge in an inner portion of the SEG portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive concept will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1A and FIG. 1B are block diagrams that illustrate conceptualdiagrams of semiconductor devices 1000, 1100, respectively;

FIG. 2 is a schematic cross-sectional view of a fin field effecttransistor (FinFET) according to an exemplary embodiment;

FIG. 3 is a schematic perspective view of a semiconductor deviceaccording to an exemplary embodiment of the inventive concept;

FIGS. 4A through 4G are cross-sectional views illustrated according to aprocess sequence to describe a method of manufacturing a semiconductordevice according to an exemplary embodiment of the inventive concept;

FIGS. 5A through 5D are cross-sectional views illustrated according to aprocess sequence to describe a method of fabricating a semiconductordevice according to an exemplary embodiment of the inventive concept;

FIGS. 6A through 6D are cross-sectional views illustrated according to aprocess sequence to describe a method of fabricating a semiconductordevice according to an exemplary embodiment of the inventive concept;and

FIGS. 7A to 7D are cross-sectional views illustrated according to aprocess sequence to describe a method of manufacturing a semiconductordevice according to an exemplary embodiment of the inventive concept.

FIG. 8 is flow chart showing a method of manufacturing a semiconductordevice according to exemplary embodiments of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the inventive concept will be described indetail with reference to the accompanying drawings.

FIG. 1A and FIG. 1B are block diagrams that illustrate conceptualdiagrams of semiconductor devices 1000, 1100, respectively.

Referring to FIG. 1A, the semiconductor device 1000 may include a memorycell array region 1010 and a peripheral circuit region 1020 which isdisposed around the periphery of the memory cell array region 1010.

A memory element may be arranged in the memory cell array region 1010.The memory element may be a static random-access memory (RAM) (SRAM), adynamic RAM (DRAM), a magnetic RAM (MRAM), a phase change RAM (PRAM),and a resistive RAM (RRAM), but the disclosure is not limited thereto.

A circuit element for driving the memory element arranged in the memorycell array region 1010 may be arranged in the peripheral circuit region1020. The circuit element may include a read circuit, a write circuit,and other control circuits, but the disclosure is not limited thereto.

Referring to FIG. 1B, the semiconductor device 1100 may include a logicregion 1110 and an SRAM region 1120.

The logic region 1110 may include various circuits and/or memoryelements combined with the circuits.

The logic region 1110 and the SRAM region 1120 are illustrated asexamples, but the embodiment is not limited thereto. Another memoryelements such as DRAM, MRAM, PRAM, RRAM, and the flash memory may beused.

FIG. 2 is a schematic cross-sectional view of a fin field effecttransistor (FinFET) according to an exemplary embodiment.

Referring to FIG. 2, a cross-sectional view of the FinFET including afirst source/drain structure 201 and a gate structure 120 formed on atop surface of a fin structure 110 is schematically illustrated. TheFinFET structure may be formed with epitaxial layers grown on asubstrate 101.

Unlike a two-dimensional (2D) planar FET, the FinFET may include aregion of the first source/drain structure 201 which is not limited byan element isolating layer 103. A profile of the first source/drainstructure 201 may be in a form of a facet. A rhombus, a hexagon, or anoctagon may be formed due to different growth rates of crystal surfacesof the epitaxial layer depending on constituent materials. The firstsource/drain structure 201 may form a contact region or a merged region(hereinafter, referred to as the contact region) with the epitaxiallayer grown adjacent to first source/drain structure 201. For example,the first source/drain structure 201 may form a source/drain assembly inwhich adjacent source/drain structures are merged with each other via a(110) crystal surface.

As a measure for improving performance of the semiconductor device inthe logic region 1110 (refer to FIG. 1B), there is a trend to form asecond source/drain structure 203 including a high concentration ofimpurities to reduce contact resistance. The high concentration ofimpurities may further promote the growth of the crystal surfacesconstituting the top side and the lateral side surfaces of the epitaxiallayer which may be (111) crystal surfaces, and thus, the contact regionbetween the adjacent second source/drain structures 203 including thehigh concentration of impurities may be reduced. Due to the reducedcontact region, defects such as cracks in the contact region may resultin subsequent processes of forming of a contact plug. As a result, thereduced contact region between the adjacent second source/drainstructures 203 including the high concentration of impurities may affectelectrical characteristics and manufacturing efficiency of asemiconductor device.

FIG. 3 is a schematic perspective view of a semiconductor device 10according to an exemplary embodiment of the inventive concept.

Referring to FIG. 3, the semiconductor device 10 may include the FinFETincluding a source/drain assembly 240 on the substrate 101.

The semiconductor device 10 may include the substrate 101, the elementisolating layer 103, the fin structures 110, the source/drain assembly240, and the gate structure 120.

In some embodiments, the substrate 101 may be a semiconductorcrystalline material (e.g., crystalline silicon wafer or crystallineSiGe wafer). For example, the substrate 101 may include silicon (Si)such as monocrystalline Si, polycrystalline Si, or amorphous Si.However, a material of the substrate 101 is not limited to Si. In someembodiments, the substrate 101 may include a Group IV semiconductor suchas germanium (Ge), a Group IV-IV compound semiconductor such as Sigermanium (SiGe) and Si carbide (SiC), or a Group III-V compoundsemiconductor such as gallium arsenide (GaAs), indium arsenide (InAs),and indium phosphide (InP).

The substrate 101 may be based on a Si bulk substrate or a silicon oninsulator (SOI) substrate. In the semiconductor device 10, the substrate101 may be based on the Si bulk substrate. In addition, the substrate101 is not limited to the bulk or the SOI substrate and may be asubstrate based on an epitaxial wafer, a polished wafer, or an annealedwafer.

Although not illustrated, the substrate 101 may include a conductiveregion, for example, a well doped with an impurity, or variousstructures doped with impurities. In addition, the substrate 101 mayform a p-type substrate or an n-type substrate depending on the kind ofdopant ions.

The substrate 101 may be classified into various regions depending onthe types of elements formed thereon. For example, the substrate 101 maybe classified into a logic region where a logic element or a computingelement is formed and a memory region where a memory element is formed.However, the regions of the substrate 101 may not be classified intoonly the logic region and the memory region.

The element isolating layer 103 may be arranged on the substrate 101with a certain height and may be formed of an insulating material. Forexample, the element isolating layer 103 may include any one of an oxidelayer, a nitride layer, and an oxynitride layer. The element isolatinglayer 103 may be arranged between the fin structures 110 to electricallyisolate each of the fin structures 110.

The fin structures 110 may have a structure in which a plurality of finstructures 110 are arranged in a first direction (X direction) andextend in parallel with each other in a second direction (Y direction)perpendicular to the first direction (X direction). The fin structures110 may have a structure which begins at the substrate 101 (correctexpression?) and extends in a third direction (Z direction)perpendicular to the first and second directions (X and Y directions).The fin structures 110 may be formed on the substrate 101 as a base.Accordingly, the fin structures 110 may include the same material as thesubstrate 101.

Impurity ions may be heavily doped on the top surfaces of the finstructures 110 on both sides of the gate structure 120 in the seconddirection (Y direction) to form the source/drain assembly 240.

The source/drain assembly 240 may be an epitaxial layer including a highconcentration of phosphorus (P) as an impurity. The source/drainassembly 240 may include an outer portion 240F and an inner portion2401. The outer portion 240F of the source/drain assembly 240 mayinclude an outer surface 240Fa and an inner surface 240Fb. The innersurface 240Fb conformally contacts the inner portion 2401 of thesource/drain assembly 240 except for a lowermost portion 240B of thesource/drain assembly 240. According to an exemplary embodiment, theouter portion 240F of the source/drain assembly 240 including the outersurface 240Fa and the inner surface 240Fb may include Si and Ge, and theinner portion 2401 of the source/drain assembly 240 may include Si butnot Ge. According to an exemplary embodiment, the lowermost portion 240Bof the source/drain assembly 240 that contacts the top surfaces of thefin structures 110 may include Si but not Ge. For example, the lowermostportion 240B, which is the lowermost portion of the inner portion 2401of the source/drain assembly 240 that contacts the top surfaces of thefin structures 110, includes Si but not Ge. In this exemplaryembodiment, the lowermost portion 240B of the source/drain assembly 240(lowermost portion of the inner portion 2401), the top surfaces of thefin structures 110 and the top surface of the element isolating layer103 are coplanar. According to an exemplary embodiment of the inventiveconcept, the semiconductor device 10 may include the source/drainassembly 240 including a contact region which has a sufficient sizewhile having a width satisfying a certain value in accordance with adesign rule. The gate structure 120 may be formed on the elementisolating layer 103 as a structure extending in the first direction (Xdirection) while covering the fin structures 110. Although only one gatestructure 120 is illustrated in FIG. 3, a plurality of gate structures120 may be formed in the second direction (Y direction). When an elementis referred herein to as being “contacting” or “in contact with” anotherelement, there are no intervening elements present.

The gate structure 120 may include a gate insulating layer 130, a workfunction control layer 140, a gate electrode 150, and a spacer 160. Thegate insulating layer 130 may cover both side surfaces and the topsurfaces of the fin structures 110 and may have a uniform thickness.

The gate insulating layer 130 may include an insulating material. Thegate insulating layer 130 may include an oxide such as silicon oxide(SiO_(x)) or a nitride such as silicon nitride (SiNx). Alternatively,the gate insulating layer 130 may include a high-k dielectric material.The gate insulating layer 130 may also be formed on the elementisolating layer 103. In other embodiments, the gate insulating layer 130may not be formed on the element isolating layer 103.

The work function control layer 140 may be formed on the gate insulatinglayer 130. The work function control layer 140 may adjust a workfunction of a transistor. In other embodiments, the work functioncontrol layer 140 may not be formed. The work function control layer 140may, as illustrated, extend upward in a direction perpendicular (Zdirection) to an upper surface of the substrate 101 along the inner sidesurfaces of the gate insulating layer 130. The work function controllayer 140 may include a metal compound. For example, the work functioncontrol layer 140 may include titanium nitride (TiN), tantalum nitride(TaN), titanium carbide (TiC), or tantalum carbide (TaC).

The gate electrode 150 may cover both side surfaces and the top surfaceof the fin structure 110 via the gate insulating layer 130. The gateelectrode 150 may extend in the first direction (X direction) like thegate structure 120. The gate electrode 150 may include polycrystallineSi or a conductive material doped on polycrystalline Si with a metalmaterial such as aluminum (Al), nickel (Ni), tungsten (W), titanium(Ti), and tantalum (Ta). In addition, the gate electrode 150 may includea metal compound such as TiN, TaN, TiC, or TaC.

The spacer 160 may be formed over both side surfaces of the gateelectrode 150. The spacer 160 may include an insulating material. Forexample, the spacer 160 may include any one of an oxide layer, a nitridelayer, and an oxynitride layer.

FIGS. 4A through 4G are cross-sectional views illustrated in a processsequence to describe a method of manufacturing a semiconductor deviceaccording to an embodiment of the inventive concept.

FIGS. 4A through 4F are cross-sectional views corresponding to across-section taken along line A-A′ in FIG. 3.

Referring to FIG. 4A, the fin structure 110 may protrude above the topsurface of the device isolating layer 103.

A semiconductor layer (not illustrated) may be formed on the substrate101. The semiconductor layer may be formed directly on, and may contactthe substrate 101. The semiconductor layer may be formed via anepitaxial growth process.

The semiconductor layer may include a material having a differentlattice constant from the substrate 101. When the substrate 101 is a Sisubstrate, the semiconductor layer may include a material having alarger lattice constant than Si or a material having a lower latticeconstant than Si.

When the semiconductor layer is used as an nFET region, thesemiconductor layer may include, for example, SiC. Alternatively, whenthe semiconductor layer is used as a pFET region, the semiconductorlayer may include, for example, SiGe.

The semiconductor layer formed on the substrate 101 may be in a fullystrained state. For example, the lattice constant of the semiconductorlayer may be the same as that of the substrate 101. A thickness of thesemiconductor layer formed on the substrate 101 may be equal to or lessthan a critical thickness so that the semiconductor layer is in thefully strained state. For example, when the semiconductor layer includesSiGe (e.g., when the semiconductor layer is used as a pFET region),fully strained state may mean that the in-plane lattice constant of theSiGe layer, which is larger than that of the Si substrate, is compressedso that it matches that of the Si substrate.

Next, the semiconductor layer and a portion of the substrate 101 may bepatterned to form the fin structure 110 on the substrate 101. The finstructure 110 may be formed on the substrate 101 so as to extend in thesecond direction (Y direction).

Next, the element isolating layer 103 may be formed on the substrate101. The element isolating layer 103 may include the material describedabove with reference to FIG. 3. The top surface of the fin structure 110and the top surface of the element isolating layer 103 may be arrangedon the same plane via a planarization process.

Next, a portion of the element isolating layer 103 may be recessed. Inthis manner, the fin structure 110 may protrude above the top surface ofthe element isolating layer 103. For example, the element isolatinglayer 103 may be formed to contact a portion of the side walls of thefin structure 110. The fin structure 110 may be defined by the elementisolating layer 103. A portion of the fin structure 110 protruding abovethe element isolating layer 103 may be defined as a top pattern 113 ofthe fin structure 110 and a remaining portion may be defined as a bottompattern 111 of the fin structure 110.

In addition, impurity doping for adjusting a threshold voltage may beperformed onto the fin structure 110. When the pFET is fabricated byusing the fin structure 110, a p-type impurity may be boron (B).Alternatively, when the nFET is fabricated by using the fin structure110, an n-type impurity may be P or As. For example, doping foradjusting the threshold voltage may be performed onto the top pattern113 of the fin structure 110 which is used as a channel region of atransistor.

Referring to FIG. 4B, the gate structure 120 intersecting with the finstructure 110 and extending in the first direction (X direction) may beformed and the bottom pattern 111 of the fin structure 110 may be formedby removing the top pattern 113 of the fin structure 110 exposed at bothsides of the gate structure 120.

Dashed lines in figures are provided for describing the elements whichexist after having recessed.

The gate structure 120 may include the gate insulating layer 130 and thegate electrode 150. In some embodiments, the gate structure 120 may beformed via a gate replacement process, but is not limited thereto.

Next, the top pattern 113 of the fin structure 110 exposed at both sidesof the gate structure 120 may be removed to form the bottom pattern 111of the fin structure 110. For example, portions of the fin structure 110that do not overlap the gate structure 120 may be removed to form therecesses on both side surfaces of the gate structure 120. A top surface111T of the bottom pattern 111 of the fin structure 110 may be arrangedon the same plane as a top surface 103T of the element isolating layer103 via the recesses.

Referring to FIG. 4C, a first source/drain layer 210 may be formed onthe bottom pattern 111 of the fin structure 110.

Respective source/drain layers 211, 213, and 215 of the firstsource/drain layer 210 may be grown separately from each other on thebottom pattern 111 of the fin structure 110 at a uniform height. In someembodiments, the first source/drain layer 210 may be grown from thebottom pattern 111 of the fin structure 110 via a selective epitaxialgrowth (SEG) process. In addition, the first source/drain layer 210 mayinclude a doped compound, such as boron (B) which is a p-type impurity,and such as phosphorus (P) which is an n-type impurity. The impurity maybe doped in a separate process, or the impurity may be doped in-situduring the epitaxial growth.

Here, a process of forming the first source/drain layer 210 in the nFETregion by doping with P, which is an n-type impurity, will be described.In some embodiments, a doping concentration of P in the firstsource/drain layer 210 may be about 1.8×10²¹/cm³ or more. As describedabove, contact resistance may be decreased by doping the firstsource/drain layer 210 with a high concentration of impurities.

As illustrated in FIG. 4C, the first source/drain layer 210 may includethree adjacent source/drain layers 211, 213, and 215 on the bottompattern 111 of the fin structure 110, but is not limited thereto.

SEG including Si and being doped with a high concentration of impuritiesmay cause sharp protrusions to the top surfaces and the side surfacesthereof. A crystal structure formed by the epitaxial growth may beformed such that the sharp protrusions from the top surfaces and theside surfaces have certain angles. However, since the crystal structuretypically tends to grow so as to have a constant aspect ratio, theaspect ratio of the epitaxial growth may be kept constant. As the firstsource/drain layer 210 grows, an area occupied by the first source/drainlayer 210 may gradually increase.

Referring to FIG. 4D, a second source/drain layer 220 may grow such thatrespective adjacent source/drain layers 221, 223, and 225 form contactregions therebetween.

For improving performance of a semiconductor device arranged in thelogic region 1110 (refer to FIG. 1), forming low contact resistancebetween adjacent source/drain layers 221, 223, and 225 is crucial. Sucha low resistance contact may be formed by adding a highly-concentratedimpurities in a source/drain structure. The high concentrated impuritiesmay further promote the growth of the crystal surfaces constituting thetop and side surfaces of the epitaxial layer which may be the (111)crystal surfaces. Because of increased growth rate of the source/drainlayers which include highly concentrated impurities, the contact regionsbetween the adjacent source/drain structures may be reduced.

Because entire width 220W of the second source/drain layer 220 in adirection parallel to the upper surface of the substrate 101 (Xdirection) may be limited to a certain value in accordance with thedesign rule of the semiconductor device, the second source/drain layer220 is also formed to have a restricted structure within the designrule. An area of contact region 220MH may be reduced as compared withthe case where the concentration of impurities is relatively low. Thelow concentration of impurities may be about 1.4e21/cm3 or less.

Such an area reduction in the contact region 220MH may cause a defectsuch as a crack in the contact region 220MH when forming a contact plugin a subsequent process. As a result, the reduced contact regions 220MHof the second source/drain layer 220 containing the high concentrationof impurities may affect the electrical characteristics andmanufacturing efficiency of the semiconductor device.

Referring to FIG. 4E, a third source/drain layer 230 may overgrow suchthat adjacent source/drain layers 231, 233, and 235 may form largercontact regions.

The third source/drain layer 230 may overgrow so as to form a contactregion 230MH to a degree similar to when the concentration of impuritiesis low. In this case, the contact region 230MH may satisfy a structuralperformance of the semiconductor device, but a width 230W of the thirdsource/drain layer 230 may be longer than a width allowed by design ruleof the semiconductor device.

The principal reason of the problem mentioned above is that the facetmay be formed on a specific crystal surface which have different growthrates compared with other crystal surfaces. For example, the growth rateon the (111) crystal surface may be lower than those on a (110) crystalsurface and a (100) surface. When the third source/drain layer 230 isfree to grow, the facet may finally have the (111) crystal surface. Forexample, the facet may exist as the (111) crystal surface. In an initialgrowth stage of the third source/drain layer 230, facets may not besufficiently formed. However, as the epitaxial growth progresses, facetsmay gradually appear due to differences in the growth rates. Thus, thecrystal surface on the side surface of the third source/drain layer 230may include the (111) crystal surface and the growth rate of thesource/drain structure may be excessive resulting in violating designrule relating with the width 230W.

Referring to FIG. 4F, the semiconductor device 10 including asource/drain assembly 240 may be formed by stopping the growth of eachof adjacent source/drain layers 241, 243, and 245 and performing anetching process.

After the third source/drain layer 230 (refer to FIG. 4E) is formed, theepitaxial growth may be stopped and the etching process may beperformed. The etching process may be performed, for example, byinjecting an etching gas, such as germane (GeH₄), into the same processchamber as the process chamber in which the epitaxial layer is formed.In some embodiments, the epitaxial growth process and the etchingprocess may be performed in an in-situ manner. For example, theepitaxial growth process and the etching process may be performed in thesame process chamber without a vacuum break therebetween.

During the etching process, Ge element included in the etching gas,GeH₄, may be bonded onto an outer portion 240F of the source/drainassembly 240. For example, the source/drain assembly 240 formed in thenFET region may be a Si epitaxial layer including P as an impurity, andconcentration of P impurity may be about 1.8×10²¹/cm³ or more. Thesource/drain assembly 240 may include the material composition andstructure described above with reference to FIG. 3, thus, will not berepeated herein. The outer portion 240F of the source/drain assembly 240may include Si and Ge therein, and the inner portion 2401 (see FIG. 3)of the source/drain assembly 240 may include Si but not Ge therein.

Because the Ge element on the source/drain assembly may change theimpurity concentration of crystal surface, the source/drain assembly 240may be formed which includes a contact region 240MH on which epitaxialgrowth rate is maintained to that of the epitaxial growth rate of lowconcentrated impurities epitaxial layer. Thus, excessive growth of thesource/drain layer may be limited to the same with the case of contactregion size of low impurity concentration while a width 240W satisfyingthe design rule of the semiconductor device 10.

During the etching process, the sharp protrusions on the top surface andthe side surface of the source/drain assembly 240 may be removed morethan a flat portion thereof. As illustrated in FIG. 4F, in across-sectional view of the source/drain assembly 240 taken along adirection parallel to the gate structure 120, each of the source/drainlayers 241, 243, and 245 may have a length 240TW of the uppermostsurface of the source/drain assembly 240 in a direction parallel to theupper surface of the substrate 101 (X direction) be etched to be lessthan a length 240SH of the side surface of the source/drain assembly 240in a direction perpendicular to the upper surface of the substrate 101(Z direction).

For example, according to exemplary embodiment, the semiconductor device10 according to the inventive concept may have improved electricalcharacteristics due to control of the epitaxial growth along the crystalsurfaces of the source/drain assembly 240 and by increasing the contactregion 240MH between adjacent source/drain layers 241, 243, and 245.

Referring to FIG. 4G, respective crystal surfaces of the source/drainassembly 240 and an angle therebetween are illustrated.

The source/drain assembly 240 may include different crystal surfacesdepending on the epitaxial growth and the etching process. The growthrate of the (111) crystal surface may be less than that of the (110)crystal surface and the growth rate of the (110) crystal surface may beless than that of the (100) crystal surface. This may be because thegrowth rate depends on surface bonding of a crystal surface. Thus, thefacet may be formed due to differences in the growth rates of differentcrystal surfaces.

Unlike the growth rate, the etching rate of the (111) crystal surfacemay be less than that of the (100) crystal surface, and the etching rateof the (100) crystal surface may be less than that of the (110) crystalsurface. This may be due to characteristics which mean that the etchingrate depends on surface bonding and in-plane bonding of the crystalsurface. Accordingly, the source/drain assembly 240 may includedifferent crystal surfaces due to different etching rates of thedifferent crystal surfaces.

In the source/drain assembly 240, a contact region 240M may be the (110)crystal surface, the uppermost surface 240T may be the (111) crystalsurface, and an inclined surface 240C connecting the uppermost surface240T and the contact region 240M may be a (311) crystal surface. Forexample, a top surface of the source/drain assembly 240 may have aV-shaped groove 240V and at least one of surfaces forming the V-shapedgroove 240V may be the (311) crystal surface.

As illustrated in FIG. 4G, in the cross-sectional view of thesource/drain assembly 240 taken along a direction parallel to the gatestructure 120, an angle θ formed by the top surface 111T of the finstructure 110 and the inclined surface 240C may be less than about54.7°. Here, an angle of about 54.7° may be an angle formed by the topsurface 111T of the fin structure 110 of the epitaxial growth includingthe low concentration of impurities and the (311) crystal surface, forexample, the inclined surface 240C. The angle θ may preferably be lessthan about 45°, via the etching process. For example, the angle θ of thesource/drain assembly 240 may in the result of performing both theepitaxial growth and the etching processes.

FIGS. 5A through 5D are cross-sectional views illustrated in a processsequence to describe a method of fabricating the semiconductor device 20according to an embodiment of the inventive concept.

Referring to FIG. 5A, a first source/drain layer 310 may be formed onthe bottom pattern 111 of the fin structure 110.

Respective source/drain layers 311, 313, and 315 of the firstsource/drain layer 310 may be grown separately from each other on thebottom pattern 111 of the fin structure 110 at a uniform height. Here, aprocess of forming the first source/drain layer 310 by doping P as animpurity in the nFET region will be described. In addition, the dopingconcentration of P may be about 1.8×10²¹/cm³ or more. In this manner,contact resistance may be reduced by doping with a high concentration ofimpurities.

As shown in FIG. 5A, the first source/drain layer 310 may include threesource/drain layers 311, 313, and 315 formed on the bottom pattern 111of the fin structure 110, but is not limited thereto.

Referring to FIGS. 5B and 5C, a second source/drain layer 320 mayinclude adjacent source/drain layers 321, 323, and 325. Next, a thirdsource/drain layer 330 may be formed in which the sharp protrusions onthe top surface and the side surfaces thereof are flattened during theetching process.

The high concentration of impurities may further promote the growth ofthe crystal surfaces constituting the top surface and the side surfacesof the epitaxial layer, for example, the (111) crystal surface, so thatthe contact regions between adjacent source/drain structures includingthe high concentration of impurities is reduced.

Thus, in order to form a large contact region, the second source/drainlayer 320 may be grown to a certain size so that the adjacentsource/drain layers 331, 333, and 335 are separated from each other, andthen, the third source/drain layer 330 may be formed by performing theetching process such that the sharp protrusions on the top surfaces andthe side surfaces thereof are flat.

A combination of the growth process and the etching process may bereferred to as a growth/etching cycle. In some embodiments, forming thethird source/drain layer 330 may include only one growth/etch cycle. Inother embodiments, the third source/drain layer 330 may be formed viatwo to five growth/etch cycles. Although not illustrated, a structureobtained via two to five growth/etch cycles may be similar to that ofthe third source/drain layer 330.

The epitaxial growth may be performed on remaining portions of an etchedepitaxial layer. In some embodiments, the etched epitaxial layer and anewly grown epitaxial layer may be comprised with the same material(e.g., the same material composition). In other embodiments, the etchedepitaxial layer and the newly grown epitaxial layer may includedifferent materials (e.g., different material compositions). A pluralityof growth/etch cycles may be repeated to further increase a region ofthe epitaxial layer. The growth/etching cycles may be performed in anin-situ manner without a vacuum break therebetween. For example, theetching process may be performed by injecting an etching gas such ashydrochloride (HCl) into the same process chamber as the process chamberin which the epitaxial layer is formed. In the growth/etching cycleprocess, Ge may not be formed on the outer surface of the thirdsource/drain layer 330 because an etching gas such as GeH₄ may not beused.

As the growth/etch cycles are repeated, a profile of the thirdsource/drain layer 330 may become more conformal.

Referring to FIG. 5D, the growth process of each of adjacentsource/drain layers 341, 343, and 345 may be stopped and a final etchingprocess may be performed in order to form the semiconductor device 20including a fourth source/drain assembly 340.

After one or more growth/etch cycle processes are performed on thesecond source/drain layer (refer to 320 in FIG. 5B) so that respectivesource/drain layers 311, 313, and 315 have certain contact regions witheach other, the epitaxial growth may be stopped and a final etchingprocess may be performed. For example, the final etching process may beperformed by injecting an etching gas such as GeH₄ into the same processchamber as the process chamber in which the epitaxial layer is formed.

During the final etching process, Ge generated in GeH₄, the etching gas,may bond to an outer portion 340F of the source/drain assembly 340. Forexample, the source/drain assembly 340 formed in the nFET region may bethe epitaxial layer including P as an impurity at a concentration ofabout 1.8×10²¹/cm³ or more, may include Si and Ge on the outer portion340F thereof, and may include Si but not Ge in an inner portion of thesource/drain assembly 340. As a result, the source/drain assembly 340may be formed so as to have a width satisfying a certain value inaccordance with the design rule of the semiconductor device 20, while avalue of the low concentration of impurities of the contact region alsois substantially the same as that of the epitaxial growth.

FIGS. 6A through 6D are cross-sectional views illustrated in a processsequence to describe a method of fabricating the semiconductor device30, according to an embodiment of the inventive concept.

Referring to FIG. 6A, a first source/drain layer 410 may be formed onthe bottom pattern 111 of the fin structure 110.

Source/drain layers 411, 413, and 415 of the first source/drain layer410 may be grown on the bottom pattern 111 of the fin structure 110 at auniform height. Here, a process of forming the first source/drain layer410 by doping P as an impurity in the nFET region will be described. Thedoping concentration of P may be about 1.8×10²¹/cm³ or more. Asdescribed above, the contact resistance may be lowered by doping with ahigh concentration of impurities.

As shown in FIG. 6A, the first source/drain layer 410 may include threesource/drain layers 411, 413, and 415 formed on the bottom pattern 111of the fin structure 110, but is not limited thereto.

Referring to FIGS. 6B and 6C, a second source/drain layer 420 mayinclude adjacent source/drain layers 421, 423, and 425, each of which isseparately grown. Next, a third source/drain layer 430 may be formed inwhich sharp protrusions on top surfaces and side surfaces of the secondsource/drain layer 420 are flattened via the etching process.

The combination of the growth process and the etching process may bereferred to as the growth/etching cycle. In some embodiments, formingthe third source/drain layer 430 may include only one growth/etch cycle.In other embodiments, the third source/drain layer 430 may be formed viatwo to five growth/etch cycles. Although not illustrated, a structureobtained via two to five growth/etch cycles may be similar to that ofthe third source/drain layer 430.

Epitaxial growth may be performed on remaining portions of the etchedepitaxial layer. In some embodiments, the etched epitaxial layer and anewly grown epitaxial layer may include the same material (e.g., thesame material composition). In other embodiments, the etched epitaxiallayer and the newly grown epitaxial layer may include differentsemiconductor materials (e.g., different material compositions). Theplurality of growth/etch cycles may be repeated to further increase aregion of the epitaxial layer. The growth/etch cycles may be performedin an in-situ manner without a vacuum break therebetween. For example,the etching process may be performed by injecting an etching gas such ashydrochloride (HCl) into a process chamber which is the same as theprocess chamber in which the epitaxial layer is formed. In thegrowth/etch cycle process, Ge may not be formed on the outer surface ofthe third source/drain layer 430 because an etching gas such as GeH₄ maynot be used.

As the growth/etch cycles are repeated, a profile of the thirdsource/drain layer 430 may become more conformal.

Referring to FIG. 6D, the growth process of respective adjacentsource/drain layers 441, 443, and 445 may be stopped and a final etchingprocess may be performed in order to form the semiconductor device 30including a source/drain structure 440.

After the third source/drain layer 430 (refer to FIG. 6C) is formed, theepitaxial growth is stopped and the final etching process is performed.For example, the etching process may be performed by injecting anetching gas, such as GeH₄, into the same process chamber as the processchamber in which the epitaxial layer is formed.

During the etching process, Ge generated in GeH₄, the etching gas, maybond to an outer portion 440F of the source/drain structure 440. Thesource/drain structure may include an impurity (e.g., an n-type impurityor an p-type impurity) in an outer portion of the source/drain structure440F and the impurity is not included in an inner portion of thesource/drain structure 440. For example, the source/drain structure 440formed in the nFET region may be the epitaxial layer including P as animpurity at a concentration of about 1.8×10²¹/cm³ or more, may includeSi and Ge on the outer portion 440F thereof, and may include Si but notGe in an inner portion of the source/drain structure 440.

Sharp protrusions of the source/drain structure 440 may be removed morethan flat portions thereof during the etching process so that eachprofile of the source/drain layers 441, 443, and 445 constituting thesource/drain structure 440 is formed into an octagonal shape.

The semiconductor device 30 may be manufactured such that contact plugsare formed on the source/drain layers 441, 443, and 445, respectively.Alternatively, the semiconductor device 30 may be fabricated to furtherinclude an element that may not be formed in the element isolating layer103 in a process performed before forming the contact plug.

FIGS. 7A to 7D are cross-sectional views illustrated in a processsequence to describe a method of manufacturing the semiconductor device40 according to an embodiment of the inventive concept.

Referring to FIG. 7A, the semiconductor device 40 may include the toppattern 113 of the fin structure 110 constituting a first source/drainlayer 510 epitaxially grown on the top pattern 113 of the fin structure110.

Since the epitaxial growth on the (111) crystal surface may be less thanthat on other crystal surfaces, the outer periphery of the firstsource/drain layer 510 may not have the same profile as an initialprofile of the top pattern 113 of the fin structure 110. Instead, theouter peripheries of the first source/drain layer 510 may extend to thetop surfaces and the side surfaces of the fin structure 110 and may formfacets. This movement may reduce spaces between the source/drain layers511, 513, and 515 growing on adjacent fin structures 110.

Referring to FIG. 7B, a second source/drain layer 520 may grow such thata contact region is formed between each of the adjacent source/drainlayers 521, 523, and 525.

A high concentration of impurities may further promote the growth of thecrystal surfaces constituting top surfaces and side surfaces of theepitaxial layer or, for example, the (111) crystal surface, such thatthe contact regions between adjacent source/drain structures includingthe high concentration of impurities are reduced.

For example, an entire width of the second source/drain layer 520 may belimited to a certain value in accordance with the design rule of asemiconductor device. When the second source/drain layer 520 is formedto satisfy the certain value, the contact regions may be reduced ascompared with a case where the impurity concentration is low.

Referring to FIG. 7C, a third source/drain layer 530 may overgrow suchthat adjacent source/drain layers 531, 533, and 535 may form largercontact regions.

The third source/drain layer 530 may overgrow so as to form the contactregions to a degree similar to a case in which the impurityconcentration is low. In this exemplary embodiment, the contact regionsmay satisfy a structural performance of the semiconductor device, but awidth of the third source/drain layer 530 may be out of a certain valuein accordance with the design rule of the semiconductor device.

Referring to FIG. 7D, the semiconductor device 40 including asource/drain assembly 540 may be formed by stopping the growth of eachof adjacent source/drain layers 541, 543, and 545 and performing anetching process.

After the third source/drain layer 530 (refer to FIG. 7C) is formed, theepitaxial growth is stopped and the etching process is performed. Forexample, the etching process may be performed by injecting an etchinggas such as GeH₄ into the same process chamber as the process chamber inwhich the epitaxial layer is formed. In some embodiments, the epitaxialgrowth process and the etching process may be performed in an in-situmanner. For example, the epitaxial growth and the etching process may beperformed in the same process chamber without a vacuum breaktherebetween.

During the etching process, Ge generated from the etching gas GeH₄ maybond to an outer portion 540F of the source/drain assembly 540. Forexample, the source/drain assembly 540 formed in the nFET region may bethe epitaxial layer including P as an impurity at a concentration ofabout 1.8×10²¹/cm³ or more, may include Si and Ge on the outer portion540F thereof, and may include Si but not Ge in an inner portion of thesource/drain assembly 540.

As a result, the source/drain assembly 540 may be formed which has awidth satisfying a certain value in accordance with the design rule ofthe semiconductor element 40 while a value of the low concentration ofimpurities of the contact regions also is substantially the same as thatof the epitaxial growth.

For example, the semiconductor device 40 according to the inventiveconcept may have excellent electrical characteristics by controlling theepitaxial growth along crystal surfaces of the source/drain assembly 540and increasing the contact regions between adjacent source/drain layers541, 543, and 545.

FIG. 8 is flow chart showing a method of manufacturing a semiconductordevice according to exemplary embodiments of the inventive concept.

In step S801, a fin structure is provided on a substrate, e.g., asemiconductor wafer W, including a negative channel field-effecttransistor (nFET) region and a positive channel field-effect transistor(pFET) region. The fin structure may be a fin structure 110 and thesubstrate may be a substrate 101 according to the exemplary embodimentsas disclosed above. The fin structure 110 may be formed on the substrate101 so as to extend in the second direction (Y direction).

In step S803, an element isolating layer is formed between adjacent finstructures. The element isolating layer may be an element isolatinglayer 103 according to the exemplary embodiments as disclosed above. Theelement isolating layer 103 may include the material described abovewith reference to FIG. 3. The top surface of the fin structure 110 andthe top surface of the element isolating layer 103 may be arranged onthe same plane via a planarization process.

In step S805, a gate structure is formed on the fin structure 110. Thegate structure may be a gate structure 120 according to the exemplaryembodiments as disclosed above. The gate structure 120 may include thegate insulating layer 130 and the gate electrode 150. In someembodiments, the gate structure 120 may be formed via a gate replacementprocess, but is not limited thereto.

In step S807, a source/drain structure is formed adjacent to the gatestructure 120. The source/drain structure may be a first source/drainstructure 201 (or the source/drain assembly 240, 340, 540 or thesource/drain structure 440) according to the exemplary embodiments asdisclosed above. In some embodiments, the source/drain structure 201formed in the nFET region may include: a top pattern 113 of the finstructure 110 which is a portion of the fin structure 110 protrudingover the element isolating layer 103; and selective epitaxial growth(SEG) portion formed on a top surface and side surfaces of the toppattern 113 of the fin structure 110.

In some embodiments, an angle between an inclined surface portion of theuppermost surface of the SEG portion and the top surface of the toppattern 113 of the fin structure 110 is less than about 54.7°, and theSEG includes Si and Ge on an outer portion of the SEG portion andincludes Si but not Ge in an inner portion of the SEG portion.

Semiconductor chips (having integrated circuits formed therein) may becut from the wafer W and form elements of semiconductor device packages.

While the inventive concept has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A semiconductor device comprising: a finstructure on a substrate including a negative channel field-effecttransistor (nFET) region; a gate structure formed on the fin structure;and a source/drain structure formed adjacent to the gate structure, thesource/drain structure being formed with an epitaxial layer n-typeimpurity, the concentration of the n-type impurity is about1.8×10²¹/cm³, and the outer portion of the source/drain structureincluding silicon (Si) and germanium (Ge), and the inner portion of thesource/drain structure including Si but not Ge, wherein an inclinedsurface portion of an uppermost surface of the source/drain structureforms an angle of less than about 54.7° with a top surface of the finstructure, wherein the source/drain structure includes a top surface anda side surface, each of the top surface and side surface being flat, andwherein both the top surface and the side surface contact the inclinedsurface portion.
 2. The semiconductor device of claim 1, wherein thesource/drain structure comprises a surface contacting adjacentsource/drain structures.
 3. The semiconductor device of claim 2, whereinthe surface contacting the adjacent source/drain structures is a (110)crystal surface.
 4. The semiconductor device of claim 3, wherein theuppermost surface of the source/drain structure is a (111) crystalsurface.
 5. The semiconductor device of claim 4, wherein, in across-section of the source/drain structure taken along a directionparallel to the gate structure, a length of the uppermost surface of thesource/drain structure is less than that of the surface contacting theadjacent source/drain structures.
 6. The semiconductor device of claim1, wherein the angle formed with the top surface of the fin structure bythe inclined surface portion is less than about 45° .
 7. Thesemiconductor device of claim 1, wherein the inclined surface portion isa (311) crystal surface.
 8. The semiconductor device of claim 1, whereinthe source/drain structure is separate from adjacent source/drainstructures.
 9. The semiconductor device of claim 8, wherein, in across-section of the source/drain structure taken along a directionparallel to the gate structure, the source/drain structure has anoctagonal profile.
 10. The semiconductor device of claim 1, wherein then-type impurity is phosphorus (P).
 11. A semiconductor devicecomprising: a fin structure on a substrate; a gate structure on the finstructure; and a source/drain structure adjacent to the gate structure,wherein the source/drain structure forms a source/drain assembly inwhich adjacent source/drain structures are merged with each other via a(110) crystal surface and the source/drain assembly includes a differentmaterial on an outer portion of the source/drain assembly which is notincluded in an inner portion of the source/drain assembly, and whereintop surfaces of the source/drain assembly comprise a V-shaped groove andat least one of surfaces forming the V-shaped groove is a (311) crystalsurface.
 12. The semiconductor device of claim 11, wherein thesource/drain assembly comprises a structure including three source/drainstructures.
 13. The semiconductor device of claim 11, wherein thesource/drain assembly comprises P as an impurity at a concentration ofabout 1.8×10²¹/cm³.
 14. The semiconductor device of claim 11, whereinthe source/drain assembly comprises silicon (Si) and germanium (Ge) onthe outer portion of the source/drain assembly, and comprises Si but notGe in the inner portion of the source/drain assembly.
 15. Asemiconductor device comprising: a fin structure on a substrateincluding an nFET region and a pFET region; an element isolating layerbetween the fin structures; a gate structure on the fin structure; and asource/drain structure adjacent to the gate structure, wherein thesource/drain structure formed in the nFET region includes: a top patternof the fin structure which is a portion of the fin structure protrudingover the element isolating layer; and a selective epitaxial growth (SEG)portion formed on a top surface and side surfaces of the top pattern ofthe fin structure, wherein an angle between an inclined surface portionof an uppermost surface of the SEG portion and the top surface of thetop pattern of the fin structure is less than about 45° , and the SEGportion includes Si and Ge on an outer portion of the SEG portion andincludes Si but not Ge in an inner portion of the SEG portion.
 16. Thesemiconductor device of claim 15, wherein the substrate and the finstructure comprise monocrystalline Si.
 17. The semiconductor device ofclaim 16, wherein the top pattern of the fin structure and the innerportion of the SEG portion comprise the same material composition. 18.The semiconductor device of claim 15, wherein, in a cross-section of thesource/drain structure taken along a direction parallel to the gatestructure, the source/drain structure comprises an octagonal profile.19. The semiconductor device of claim 15, wherein the SEG portioncomprises P as an impurity at a concentration of about 1.8×10²¹/cm³.